The immobilization of Sr(ll) and Co(ll) via magnetic easy-separation organophosphonate-hydroxyapatite hybrid nanoparticles

The magnetic Hexamethylene diamine tetramethylene phosphonic acid (HDTMP)-hydroxyapatite nanoparticles (HD-MHAP) were firstly prepared and applied for the immobilization of radioactive Sr 2+ (Strontium ion) and Co 2+ (Cobalt ion). The molar ratio of organic phosphine in HDTMP to total phosphorus was 10% (10HD-MHAP) and can also be easily separated from aqueous solution. At the equilibrium concentration of Sr 2+ and Co 2+ (200 mg/L), the adsorption capacity of MHAP and 10HD-MHAP on Co 2+ was 28.4 mg/g and 172.3 mg/g, respectively and for Sr 2+ , the adsorption capacity was 54.9 mg/g and 320.7 mg/g. Additionally, the desorption percentage of Sr 2+ (%) and Co 2+ (%) was very low, which was 0.66 and 1.61, respectively. This is significant because the irreversible adsorption of HDTMP/Fe 3 O 4 /HAP composite for Sr 2+ and Co 2+ ensures the captured radionuclides will not be released back into the aquatic systems. Moreover, the affinity between HDTMP and HAP and the coordination of HDTMP and Sr 2+ or Co 2+ was probed by Multiwfn wavefunction analysis. The results indicated that the formation of a ternary surface complex of MHAP-HDTMP-M (Sr 2+ or Co 2+ ) was the key to the excellent immobilization performance of HD-MHAP composite for Sr 2+ or Co 2+ .